[Bug 2022927] [NEW] Busybox mount fails to mount Snaps

[Isaac True]

Public bug reported:

Snapd tries to mount squashfs Snaps with non-standard mount flags like
"x-gdu.hide" and "x-gvfs-hide", both of which are used to indicate to
userspace programs that a given mount should not be shown in a list of
mounted partitions/filesystems. Busybox does not support these flags,
and so fails with "Invalid argument".

$ sudo busybox mount -t tmpfs -o x-gdu-hide test /tmp/test
mount: mounting test on /tmp/test failed: Invalid argument

These flags can likely be be safely ignored, as they don't actually
affect the functionality of the mount. This goes for all mount options
starting with "x-", as these generally denote non-standard mount option
"extensions".

I've created a patch against Busybox which adds an optional
configuration item to ignore all mount options beginning with "x-". An
additional verbose option has also been added to enable the ability to
report that the mount flags have been ignored, rather than silently
ignoring them.

This is a requirement for a customer project, where we are limited to
using Busybox (due to coreutils' GPL-3.0 licence) but would also require
using Snaps like checkbox for testing and verification. This was posted
on the Busybox mailing list a few months ago
(http://lists.busybox.net/pipermail/busybox/2023-March/090202.html) but
patch acceptance there seems to take quite a long time, and we need this
for the customer.

A PPA containing the patched Busybox version is available on the
project's Launchpad team: https://launchpad.net/~nemos-
team/+archive/ubuntu/ppa

** Affects: busybox (Ubuntu)
     Importance: Undecided
         Status: New

** Patch added: "busybox-1.35.0-4ubuntu1ppa5.debdiff"
   https://bugs.launchpad.net/bugs/2022927/+attachment/5677880/+files/busybox-1.35.0-4ubuntu1ppa5.debdiff

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https://bugs.launchpad.net/bugs/2022927

Title:
  Busybox mount fails to mount Snaps

Status in busybox package in Ubuntu:
  New

Bug description:
  Snapd tries to mount squashfs Snaps with non-standard mount flags like
  "x-gdu.hide" and "x-gvfs-hide", both of which are used to indicate to
  userspace programs that a given mount should not be shown in a list of
  mounted partitions/filesystems. Busybox does not support these flags,
  and so fails with "Invalid argument".

  $ sudo busybox mount -t tmpfs -o x-gdu-hide test /tmp/test
  mount: mounting test on /tmp/test failed: Invalid argument

  These flags can likely be be safely ignored, as they don't actually
  affect the functionality of the mount. This goes for all mount options
  starting with "x-", as these generally denote non-standard mount
  option "extensions".

  I've created a patch against Busybox which adds an optional
  configuration item to ignore all mount options beginning with "x-". An
  additional verbose option has also been added to enable the ability to
  report that the mount flags have been ignored, rather than silently
  ignoring them.

  This is a requirement for a customer project, where we are limited to
  using Busybox (due to coreutils' GPL-3.0 licence) but would also
  require using Snaps like checkbox for testing and verification. This
  was posted on the Busybox mailing list a few months ago
  (http://lists.busybox.net/pipermail/busybox/2023-March/090202.html)
  but patch acceptance there seems to take quite a long time, and we
  need this for the customer.

  A PPA containing the patched Busybox version is available on the
  project's Launchpad team: https://launchpad.net/~nemos-
  team/+archive/ubuntu/ppa

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